Abstract:Methods to determine hippuric acid and benzoic acid in yak milk and its products had been established by high performance liquid chromatography.The contents of hippuric acid and benzoic acid in Yak nipple milk，mixed milk and yak dairy products were determined.The relationship between the contents of hippuric acid and benzoic acid in yak milk was analyzed.The factors including microorganism，temperature and time were also monitored.The experimental results showed that there was a certain amount of hippuric acid in Yak milk，but no benzoic acid was detected.Hippuric acid and benzoic acid were detected in Yak dairy products.During the storage，hippuric acid was biodegraded to benzoic acid under the action of microorganism，which was the main source of benzoic acid in Yak milk.Microorganism，temperature and storage time were the critical factors affecting the relationship between hippuric acid and benzoic acid in Yak milk，especially microorganism.